The distribution of (Na+ + K+)ATPase is continuous along the axolemma of unensheathed axons from spinal roots of ‘dystrophic’ mice

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Abstract
(Na++K+)ATPase-like immunoreactivity along the axolemma of sensory and motor neurons and the plasmalemma of Schwann cells from spinal roots of dystrophic mice (129 ReJ Dy/Dy) was determined using polyclonal antibodies specific for guinea pig renal (Na++K+)ATPase (GP-17), along with polyclonal (439-2) and monoclonal (9A5) antibodies specific for rat renal (Na++K+)ATPase. In normal and dystrophic mice, (Na++K+)ATPase-like immunoreactivity was observed along the axolemma at nodes of Ranvier using GP-17 and 439-2, each of which binds to isozymes of (Na++K+)ATPase composed of the α and α+ forms of the catalytic subunit. Staining was not seen along the nodal axolemma with 9A5, a preparation that binds to the α form of the catalytic subunit. The terminal processes and microvilli of Schwann cells were stained using all three antibody probes. The axolemma of unensheathed axons in dystrophic mice was continuously and uniformly labelled with GP-17 and 439-2, but not 9A5. Concentrations of (Na++K+)ATPase-like immunoreactivity along Schwann cell processes were observed most often in areas adjacent to unensheathed axolemma. At heminodes, staining abruptly decreased along Schwann cell processes in areas that were separated from the unensheathed axolemma by other intervening Schwann cell processes. It was concluded from these data that in dystrophic mice (Na++K+)ATPase is uniformly distributed along unensheathed portions of axons without evidence of detectable focal concentations of the enzyme, and that the catalytic subunit of (Na++K+)ATPase along unensheathed axons is distinct from the α form found in Schwann cells and other organs. In addition, (Na++K+)ATPase is concentrated along the plasmalemma of Schwann cells in regions of close apposition to axolemmal areas associated with large ionic fluxes.